1. Field of the Invention
The present invention relates to an apparatus for automatically welding the circumferences of pipes which are laid in horizontal positions so that they may be jointed.
2. Description of the Prior Art
As the welding apparatus of the above kind, there has been known in the art a tungstem inert-gas arc welding apparatus which is usually abbreviated to "TIG wedling apparatus". This TIG welding apparatus is constructed, for example, of two arcuate frames, which are detachably connected at their two portions thereby to form a ring shape, and a welding torch, a wire feeder, a running truck, and clamping mechanisms, all of which are integrally attached to those arcuate frames. The clamping mechanisms are used to clamp the outer circumferences of the pipes. On the other hand, the running truck, and the welding torch and the wire feeder are mounted on the different arcuate frames so that they can be separated. With this construction, the welding operation is performed while the aforementioned running truck is being made to run in the circumferential direction.
However, the conventional apparatus thus constructed is not equipped with a shock absorbing mechanism for absorbing the vertical vibrations resulting from the roughnesses on the outer circumferences of the pipes and has a defect that the spacing between the leading end of the welding torch and the pipes cannot be maintained constant. Moreover, in case the body of the apparatus constructed of those two arcuate frames is to be attached to the outer circumferences of the pipes, the clamping mechanisms of the conventional apparatus are of manual type so that they cannot enjoy an excellent working property and have a defect that they cannot be mounted in desired positions with ease.
Still moreover, the aforementioned running truck carries the welding torch, the wire feeder, a profiling unit and so on, but is so constructed as to perform the welding operation in one direction while being fed with only one wedling wire. As a result, if multi-layered welding operations of several times are performed in one direction, the torch, driving power supply cables, a cooling water hose, an inert gas hose and so on will wind themselves round the pipes. In addition, the automatic welding operation is characterized to have a tendency that the bed width becomes small and the penetration becomes deep when the welding torch ascends whereas the bead width becomes large and the penetration becomes shallow when the torch descends. As a result, in the multi-layered welding operations, the differences between the ascent and descent are accumulated and enlarged so that the welding conditions have to be highly precisely controlled in order to perform the satisfactory welding operations. In order to obviate the aforementioned tendency, therefore, it is necessary either to restore the starting point, after the welding operation of one turn, thereby to restart the welding operation of another turn or to move a wire fed guide to the opposite side after the welding operation of the one turn. In either event, there arises another defect that much labor is required to deteriorate the working property.